Telephone solicitations are a nuisance. To reduce the nuisance, telephone companies provide services, such as selective-call-acceptance and selective-call-blocking. However, these services require the telephone subscriber to provide a list of telephone numbers to be accepted, or blocked.
Sometimes the list can be amended later, and sometimes the amending process is simple, because automated. For example, after an unwanted call is received, some telephone companies allow the subscriber to press a specific set of keys on the telephone, to add the caller's telephone number to the list of forbidden numbers. A similar procedure can apply to adding a caller's number to a list of acceptable numbers.
Despite the ease of amending the lists, the requirement of providing a list initially is seen as a deterrent to using these services. Two primary reasons are (1) the effort required to generate the list and (2) the fear of omitting important telephone numbers from the lists. As to reason (2), in the case of selective-call-acceptance, the fear is omitting an important person, such as a forgotten relative. In the case of selective-call-rejection, the fear is not knowing all the telephone numbers which should be rejected.
Further, even if the list(s) are generated, and the services implemented, these services do not necessarily provide complete protection. If they rely on “caller ID” information to block a call, then callers can block that identification, or use different telephone numbers at different times, and defeat the call blocking.